Ferroelectric ceramic materials

ABSTRACT

FERROELECTRIC CERAMIC MATERIALS HAVING ESSENTIALLY THE COMPOSITION PB(ZR-TI)O3 OR PB(ZR-TI-SN)O3 AND CONTAINING BI AND NB IN SMALL PERCENTAGE EXHIBIT IMPROVED COUPLING COEFFICIENTS. AS MODIFICATIONS, THE MATERIALS MAY ALSO CONTAIN MN IN SMALL PERCENTAGE AND PART OF THE PB MAY BE REPLACED BY BA, SR OR BOTH. THE MATERIALS ARE PARTICULARLY USEFUL AS CERAMIC WAVE FILTERS AND PIEZOELECTRIC VOLTAGE SOURCES.

May 25, 1971 Filed Nov. 10, 1969 CHIYOSHI OKUYAMA TAL FERROELECTRIC CERAMIC MATERIALS s sheets-sheet 1 FIG.`

o 7 d2 O4 A o6 1.o 0.6 0.6 0.4

w1/o 131203 w1 Nb205 CHIYOSHI OKUYAMA ETAL FERROELECTRIC CERAMIC MATERIALS l `3 Sheets-Sheet 2 May 25., 1971 Filed Nov. 10, 1969 United States Patent O 3,580,846 FERROELECTRIC CERAMIC MATERIALS Chiyoshi Okuyama, 2-14 Nishiki-cho, and Syuzo Osumi,

1-15 Hikari-cho, both of Fujinomiya-shi, Shizuokaken, Japan Filed Nov. 10, 1969, Ser. No. 875,368 Int. Cl. C04b 35/46, 35/48 U.S. Cl. 252-62.9 4 Claims ABSTRACT F THE DISCLOSURE Ferroelectric ceramic materials having essentially the composition Pb(Zr-Ti)03 or Pb(Zr-Ti-Sn)03 and containing Bi and Nb in small percentage exhibit improved coupling coeflicients. As modifications, the materials may also contain Mn in small percentage and part of the Pb may be replaced by Ba, Sr or both. The materials are particularly useful as ceramic wave filters and piezoelectric voltage sources.

those prepared by replacing part of the lead with strontium and/or barium which may be represented by the general formulae:

There are also known other types of ceramic materials wherein there are incorporated in the aforementioned basic components various additives, for example, metal oxides in order to improve the electrical properties of said ceramic materials such as electromechanical coupling coefficient Kp and dielectric constant e. However, the prior are ceramic materials failed to meet requirements for Kp and e, no matter what kind of additives were contained.

The present invention provides new ceramic materials that can display a more desirable values of coupling coefficient Kp and dielectric constant e than the known types similarly containing lead zirconate and lead ttanante.

The ceramic material of the present invention may include 0.04 to 1.0 percent by weight of manganese as equivalent to MnO2. When incorporatedwith manganese, the ceramic material retains the elevated degree of Kp attained by addition of bismuth and niobium and exhibits a prominently high level of QM.

This invention can be lmore fully understood from the followingy detailed description when taken in connection with reference to the accompanying drawings, in which:

FIG. 1 is a graph showing changes in the Kp and e of a ferroelectric ceramic material according to the present invention where the ratio of Bi2O3 to Nb2O5 contained therein is varied;

FIG. 2 is a graph indicating changes in the Kp and e of another ferroelectric material according to the present invention prepared from a different kind of basic component from that of FIG. l where the ratio of Bi2O3 to Nb205 contained therein is varied;

FIG. 3 graphically represents the varied properties of 3,580,545 Patented May 25, 1971 ice the present ferroelectric ceramic material corresponding to the varied content of MnO2',

FIG. 4 graphically indicates the varied properties of the present ferroelectric ceramic material containing MnOZ where the ratio of Bi2O3 to Nb2O5 contained therein is varied;

FIG. 5 is a y,graph showing changes in coupling coefficient and output voltage of the present ferroelectric ceramic material corresponding to the number of impacts applied thereto in comparison with those of the prior art ceramic material;

FIG. 6 is a graph illustrating changes in the resonance frequency of the present ferroelectric ceramic material corresponding to its temperature in comparison with those of the prior art ceramic material; and

FIG. 7 is a graph indicating changes in the resonance frequency of the present ferroelectric ceramic material corresponding to a length of time after polarization in comparison with those of prior art ceramic material.

The basic component applicable to the present invention has essentially the same composition as the known lead titanate-lead zirconate type. Less than 20 atomic percent of the lead maybe replaced by strontium and/0r barium, and also less than 20 atomic percent of the zirconium may be substituted by tin.

The ceramic material of the present invention may be prepared in the following manner. There are rst mixed in a prescribed mol ratio lead oxide, zirconium oxide and titanium oxide, and strontium oxide, barium oxide and tin oxide used if required and additives such as bismuth oxide, niobium oxide and manganese dioxide. While said mixing may be conducted either by the wet or dry process, it is preferred for fully uniform mixing to continue said mixing in a ball mill or the like for a relatively long time, say, about 5 to 10 hours. Generally, it is preferable that the lead oxide is used about 0.1 mol percent in excess of the desired ratio in order to compensate the loss caused by its evaporation on sintering. If ground in advance by the wet process, the mixture is dried and ground again and there is added thereto a suitable amount of binder.

Then the mass is formed into a desired shape at a relatively low pressure of about l ton/ cm?. The shaped body is preliminarily baked in an adequate oven such as a tunnel furnace at a relatively low temperature of, for example, 900 to ll00 C. The mass is further pulverized into suitable particle sizes of, for example, less than 20 microns, using again a ball mill or vibration mill. To the powder obtained is again added a suitable amount of binder. The mass is formed into a desired shape at a pressure of 2 to 3 ton/ cm.2 and sintered at a temperature of 1240 to l340 C. The sintered body is lapped, if required, until both sides thereof attain a prescribed degree of parallelism and flatness. To each lapped plane is tted a silver electrode by suitable means, for example, baking. This element is polarized in an insulating liquid such as silicone oil by impressing across the electrodes such as a voltage as to obtain a D.C. eld strength of, for example, about 3 to 4 kv./ mm. at normal temperature or at around C.

It has been discovered that addition of bismuth and niobium to the ferroelectric ceramic material of the present invention elevates its Kp. Experiments show that a ferroelectric ceramic material prepared by adding to the aforesaid basic component 0.2 to 3.0 percent by weight of bismuth as equivalent to Bi2O3 and 0.2 to 3.0 percent by weight of niobium as equivalent to Nb205 increased the Kp inherent to the basic component by about 20 percent or more.

While the ratio of bismuth to niobium affects to a certain extent the improvement of the Kp of the resultant ceramic material, an optimum ratio is mainly dened by the composition of the basic component. FIG. 1 shows changes in the Kp and e of several kinds of ceramic materials prepared by adding to the basic component having a composition expressed by the following chemical formula Pbosasonaaoz(Zfo.54To.4e)O3 Bi2O3 and Nb2O5 in various ratios in such a manner that the total content of both additives always accounts for 1 percent by weight on the basis of the basic component. It will be apparent from this ligure that a maximum Kp is realized by a ceramic material prepared by adding Bi2O3 and Nb205 in an equal Weight ratio. FIG. 2 represents changes in the Kp and e of several kinds of ceramic materials prepared by adding to the basic component having a composition represented by the following chemical formula PbdssgfomB a0.12 (zrasasTioAs) O3 Bi2O3 and Nb2O5 in various ratios in such a manner that the total content of both additives always accounts for l percent by weight on the basis of the basic component. In this case, as shown in FIG. 2, a ceramic material containing about 0.3 percent by weight of Bi2O3 and about 0.7 percent by weight of Nb205 has a maximum Kp.

FIG. 3 indicates the eifect on Kp, QM and e of manganese when it is added to the ferroelectric ceramic material of the present invention. The data given in FIG. 3 were obtained from various samples prepared by adding 1.0 percent by weight of Bi2O3 and 0.5 percent by weight of Nb205 to a basic component having a composition represented by a chemical formula with only MnO2 added in varying amounts. Each sample was formed by the aforementioned process into a disc 20 mm. in diameter and 0.5 mm. thick. As seen from FIG. 3, increased addition of MnO2 did not Widely vary Kp, whereas QM indicated a high value of about 1200 when said addition amounted to about 0.35 percent by weight. With respect to improvement of QM, it has been found that addition of less than about 0.05 percent by weight of MnO2 did not have a prominent effect, and conversely addition of more than 1 percent by Weight of Mn02 considerably reduced such effect.

FIG. 4 illustrates changes in the Kp, e and QM of several samples prepared Vby adding to the aforesaid basic component 0.4 percent by weight of Mn02 and further Bi203 and Nb205 in various ratios in such a manner that 4 examples. Throughout the examples, percent denotes percent by weight.

EXAMPLE 1 There were prepared two samples and four reference samples listed in Table 1 below by mixing the oxides of the elements given therein in a prescribed ratio, followed by shaping and sintering. Each sample and reference sample was prepared by grinding and mixing the powdered oxides in a ball mill for about 10 hours. A mass formed into a desired shape after addition of a suitable amount of binder was preliminarily baked at a temperature of about l000 C. and pulverized again in a ball mill. After addition of a suitable amount of binder a second time, the powder obtained was shaped into a disc 2O mm. in diameter and 0.5 mm. thick at a pressure of about 3 ton/ cm.2. Each sample was finished by being sintered for about an hour at a temperature of about l300 C. The sample was lapped on both sides before its properties were determined. After washing, each lapped plane was fitted with a silver electrode by baking. The sample was polarized in a silicone oil at about 100 C. by impressing across both electrodes such a D C. voltage as to generate a D.C. eld strength of 4 kv./mm. therein. It will be noted that throughout this and following examples, the samples having a composition specified by the present invention are designated as A and those outside of its scope as B.

As apparent from Table l above, addition of both bismuth and niobium is recognized to have a more prominent eect on the elevation of Kp than in the case where they are use singly.

EXAMPLE 2 There were prepared samples having such compositions as shown in Table 2 below under the same conditions as in Example l.

TABLE 2 the total content of both additives always accounted for l percent by weight on the basis of the basic composition.

The ceramic material of the present invention containing bismuth, niobium and manganese has the advantage that is `generates a high output voltage when used as a piezoelectric voltage source element, and that even after it is subjected to impacts a large number of times, its original impact resistance is little reduced. Further advantages of this ceramic material are that its resonance frequency is extremely stable with respect to temperature changes and a lapse of time after polarization. This obviously proves that the ceramic material of the present invention has excellent properties as a ceramic wave filter.

Features and further advantages of the present inven- EXAMPLE 3 There were prepared sample A-7 having composition Pbo.95s1'o.o5(ZI'dMToAe) Orl-05 152034-015 and reference sample B-7 having the same composition tion will be more clearly understood from the following as above except for the omission of MnOZ in the same manner as in Example l. Both samples A-7 and B-7 were formed into a rod 5 mm. in diameter and 10 mm. long and placed in a case made of plastics material. They Were repeatedly subjected to impacts of a fixed strength to determine changes in the output voltage and coupling coand sample B-9 having a composition Pb (ZI`'53T047)O3+0.45 M1102 As apparent from FIG. 6, sample A-13 represented by a dot-dash line has a preferable nature that its resonance eicient Kt in the direction of thickness corresponding ffetluefley S little aeeted by tempefatufeo of gais .elle .651.3255tifafriaffrettata?sae ein7 presente in e so i ines o t is gure n represent data on sample A-7 and the dot-dash lines those Sgondin t0 a laPlSe f 1t13me attel'dpelfizatieflli Ttle figure on sample B-7. As apparent from the ligure, the output S OWS t at Samp e feta-lne SU Stantfa Y t e Same voltage of Sample B 7 prominently decreased with the l0 resonance frequency as right after polarlzatlon even When increaing number of impacts, whereas that of sample 101%?, lotufs helwe Pessed thereafter- A7 Was reduced Very little. Further, the Kt of sample a We C 31m 1S: B-7, though initially high, decreased to about 90 percent 1 A frffelectl'ic Ceramic material having a COmPOSi' of its original value after receiving impacts 120,000 times, 15 t1 0 n conslstmg essen'flauy of, a baslc component O f lead of @j a; a ne a; .csigaydat :s anagrafe-.t2 a correspon mg to a out percent o its initia eve, lijven fafter said sample Was subjected to the same num- Oarlhbzas aos;ll;cblolnfalge; er o im acts. 3

p the same basis as equivalent to Nb205.

EXAMPLE 4 2. A ferroelectric ceramic material according to claim 1 wherein less than 20 atomic percent of the lead is re- There were prepared live samples llsted 1n Table 3 beplaced by at least one element selected from the group low 1n the same mannerl as in Example l. These samples Consisting of barium and strontium. h ad till@ Same-e01f1POS1t10I1S eX eePt1I1g that the latlO 0f 25 3. A erroelectric ceramic material according to claim z1rcon1um to tltanium was var1ed. All the samples con- 1 wherein less than 20 atomic percent of the zirconium tained 1.0% Bi2O3, 0.5% Nb205 and 0.45% MnO2. is replaced by tin.

TABLE 3 K Sample Basic compostiion (percentl e tan QM Pba.95Srn.05(Zl`a.47Ti0.53)0a 39 680 0.7 1, 750 Pb0.05S1`0.05(Z10.50Ti0.50)03 47 900 0.6 1,150 .Arlo Pbumsl'0.05(Z1`0.53TO.47)O3 62 1, 300 0.6 900 A.-ll Pbq.q5Sl'0.05(Zlu.5Tiu'44)O3 55 650 0.9 980 A-12 Pbowssrons(Zrq.5oTio.41)03 45 500 3.0 1,050

The above table shows that though the varied ratio of 4. A ferroelectric ceramic material according to claim Zr to Ti resulted in certain differences in the properties 1 wherein said composition further contains 0.04 to 1.0 of a ceramic material, samples A-4 to A-8 all displayed percent by Weight of manganese on the basis of said basic a high degree of Kp and QM. 40 component as equivalent to MnOZ.

EXAMPLE 5 References Cited There was prepared in the same manner as in Example UNITED STATES PATENTS 1 Sample A 13 having a Composition 2 911 370 11/1959 Ku1csar 252 62 9 Pboasfws(ZfoaaTiw)@fre-5% B20a+05% 45 1172094 1/1964 Roup et1. :253-62.9 Nb205+04% M1102 3,464,924 9/1969 Bann@ et al. 252-629 The sample Was tested to determine changes in the resonance frequency (f0=110 kHz.) corresponding to its tem- TOBIAS E' LEVOW Primary Examiner perature, the results being given in FIG. 6. For compari- 1 COOPER, Assistant Examiner son the gure also indicates the property associated With temperature change as exhibited by sample B-S having a U.S. Cl. X.R. l06-39R 

